Fatigue, psychological and cognitive impairment following transient ischaemic attack and minor stroke: a systematic review.

Transient ischaemic attack (TIA) and minor stroke are characterized by short-lasting symptoms; however, anecdotal and empirical evidence suggests that these patients experience ongoing cognitive/psychological impairment for which they are not routinely treated. The aims were (i) to investigate the prevalence and time course of fatigue, anxiety, depression, post-traumatic stress disorder(PTSD) and cognitive impairment following TIA/minor stroke; (ii) to explore the impact on quality of life (QoL), change in emotions and return to work; and (iii) to identify where further research is required and potentially inform an intervention study. A systematic review of MEDLINE, EMBASE, PSYCINFO, CINAHL, the Cochrane libraries and the grey literature between January 1993 and April 2013 was undertaken. Literature was screened and data were extracted by two independent reviewers. Studies were included of adult TIA/minor stroke participants with any of the outcomes of interest: fatigue, anxiety, depression, PTSD, cognitive impairment, QoL, change in emotions and return to work. Random-effects meta-analysis pooled outcomes by measurement tool. Searches identified 5976 records, 289 were assessed for eligibility and 31 studies were included. Results suggest high levels of cognitive impairment and depression post-TIA/minor stroke which decreased over time. However, frequencies varied between studies. Limited information was available on anxiety, PTSD and fatigue. Meta-analysis revealed that the measurement tool administered influenced the prevalence of cognitive impairment: Mini-Mental State Examination 17% [95% confidence interval (CI) 7, 26]; neuropsychological test battery 39% (95% CI 28, 50); Montreal Cognitive Assessment 54% (95% CI 43, 66). There is evidence to suggest that TIA/minor stroke patients may experience residual impairments; however, results should be interpreted with caution because of the few high quality studies. Notwithstanding, it is important to raise awareness of potential subtle but meaningful residual impairments.

On the multiple functional roles of the active site histidine in catalysis and allosteric regulation of Escherichia coli glucosamine 6-phosphate deaminase.

The active site of glucosamine-6-phosphate deaminase (EC 3.5.99.6, formerly 5.3.1.10) from Escherichia coli was first characterized on the basis of the crystallographic structure of the enzyme bound to the competitive inhibitor 2-amino-2-deoxy-glucitol 6-phosphate. The structure corresponds to the R allosteric state of the enzyme; it shows the side-chain of His143 in close proximity to the O5 atom of the inhibitor. This arrangement suggests that His143 could have a role in the catalysis of the ring-opening step of glucosamine 6-phosphate whose alpha-anomer is the true substrate. The imidazole group of this active-site histidine contacts the carboxy groups from Glu148 and Asp141, via its Ndelta1 atom [Oliva et al. (1995) Structure 3, 1323-1332]. These interactions change in the T state because the side chain of Glu148 moves toward the allosteric site, leaving at the active site the dyad Asp141-His143 [Horjales et al. (1999) Structure 7, 527-536]. In this research, a dual approach using site-directed mutagenesis and controlled chemical modification of histidine residues has been used to investigate the role of the active-site histidine. Our results support a multifunctional role of His143; in the forward reaction, it is involved in the catalysis of the ring-opening step of the substrate, glucosamine 6-P. In the reverse reaction, the substrate fructose 6-P binds in its open chain, carbonylic form. The role of His143 in the binding of both glucosamine 6-P and reaction intermediates in their extended-chain forms was demonstrated by binding experiments using the reaction intermediate analogue, 2-amino-2-deoxy-D-glucitol 6-phosphate. His143 was also shown to be a critical residue for the conformational coupling between active and allosteric sites. From the pH dependence of the reactivity of the active site histidine to diethyl dicarbonate, we observed a pK(a) change of 1.2 units to the acid side when the enzyme undergoes the allosteric T to R transition during which the side chain of Glu148 moves toward the active site. The kinetic study of the Glu148-Gln mutant deaminase shows that the loss of the carboxy group and its replacement with the corresponding amide modifies the k(cat) versus pH profile of the enzyme, suggesting that the catalytic step requiring the participation of His143 has become rate-limiting. This, in turn, indicates that the interaction Glu148-His143 in the wild-type enzyme in the R state contributes to make the enzyme functional over a wide pH range.

Tyr254 hydroxyl group acts as a two-way switch mechanism in the coupling of heterotropic and homotropic effects in Escherichia coli glucosamine-6-phosphate deaminase.

The involvement of tyrosine residues in the allosteric function of the enzyme glucosamine 6-phosphate deaminase from Escherichia coli was first proposed on the basis of a theoretical analysis of the sequence and demonstrated by spectrophotometric experiments. Two tyrosine residues, Tyr121 and Tyr254, were indicated as involved in the mechanism of cooperativity and in the allosteric regulation of the enzyme [Altamirano et al. (1994) Eur. J. Biochem. 220, 409-413]. Tyr121 replacement by threonine or tryptophan altered the symmetric character of the T --> R transition [Altamirano et al. (1995) Biochemistry 34, 6074-6082]. From crystallographic data of the R allosteric conformer, Tyr254 has been shown to be part of the allosteric pocket [Oliva et al. (1995) Structure 3, 1323-1332]. Although it is not directly involved in binding the allosteric activator, N-acetylglucosamine 6-phosphate, Tyr 254 is hydrogen bonded through its phenolic hydroxyl to the backbone carbonyl from residue 161 in the neighboring polypeptide chain. Kinetic and binding experiments with the mutant form Tyr254-Phe of the enzyme reveal that this replacement caused an uncoupling of the homotropic and heterotropic effects. Homotropic cooperativity diminished and the allosteric activation pattern changed from one of the K-type in the wild-type deaminase to a mixed K-V pattern. On the other hand, Tyr254-Trp deaminase is kinetically closer to a K-type enzyme and it has a higher catalytic efficiency than the wild-type protein. These results show that the interactions of Tyr254 are fundamental in coupling binding in the active site to events occurring in the allosteric pocket of E. coli glucosamine 6-P deaminase.